Stormwater wetland design criteria

Stormwater Wetland Design Criteria
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Design Criteria	Shallow Wetland	Pond/Wetland	ED Shallow Wetland*
Wetland/Watershed Ratio (Ac/Ac)	0.2	0.1	0.1
Minimum Drainage Area (Ac)	25	10	25
Length to Width Ratio (minimum)(ft/ft)	2:1	2:1	2:1
Extended Detention (ED)	No	Optional	Yes
Allocation of Vwq (pool/marsh/ED) in %	25/75/0	70/30/0(includes pond volume)	25/25/50
Allocation of Surface Area (deepwater/low marsh/high marsh/semi-wet) in %	20/35/40/5	45/25/25/5 (includes pond surface area)	10/35/45/10
Forebay	Required	Required	Required
Micropool	Required	Required	Required
Outlet Configuration	Reverse-slope pipe or hooded broad-crested weir	Reverse-slope pipe or hooded broad-crested weir	Reverse-slope pipe or hooded broad-crested weir

*Note: The ED Shallow Wetland design guidance does not meet the MPCA requirements for permanent volume. The guidance may be applied in a stormwater retrofit situation where area requirements preclude the use of a Shallow Wetland